Foot operated controls for musical instruments and the like have been configured in various well known mechanical forms; for example, a basic approach utilizes a conventional rotary potentiometer operated by a rocker foot pedal driving the potentiomenter via a rack and pinion gear mechanism.
In some versions of such a basic approach, the audio channel to be controlled was routed directly through the potentiometer; however with advanced electronic technology it has become customary to equip the foot control with only a variable resistance, biased by d.c. to develop a variable voltage which is applied to a voltage controlled amplifier or attenuator in a controller unit.
Generally, conventional rotary rheostats and rocker pedals are subject to deterioration and failures of mechanical moving parts and wiping contact surfaces with time and usage. Also the rocker mechanism ordinarily requires that the pedal be located well above the floor level, resulting in inconvenience and discomfort to the user.
Efforts to overcome the aforementioned drawbacks have led to layered structures in which conventional mechanical moving parts have been eliminated; in one known approach, pressure is applied to a pressure sensitive resistive element via a resilient cover. Such structures normally depend on pressure sensitivity properties of particulate materials, as exemplified in U.S. Pat. No. 4,314,227 to Eventoff.
Generally, in transducers which depend on the pressure sensitive properties of particulate resistive composition materials, considerable difficulty has been experienced in seeking to formulate these materials in sufficiently stable form: repeated compression and relaxation of the material tends to alter its resilience, resistance and/or pressure sensitivity and thus degrade the transducer's performance with time and usage.
Systems of the type addressed by this invention often require a somewhat customized overall input-to-output control response characteristic curve, covering a sufficient dynamic range, to satisfy human and/or equipment factors. Since the overall pressure-to-attribute response curve results from the combination of the transducer's pressure-to-voltage response curve (with constant current) and the electronic circuit's voltage-to-attribute response curve, either or both of these may be modified in attempting to satisfy the overall requirements.
A predominant class of transducers of known art are designed and configured exclusively for mass production, where initial development is hampered by considerable investments in artwork and tooling, and manufacturing demands complex and expensive mass processes such as photo-etching. Thus a particular design and response curve tend to become "frozen", leaving little or no capability in the rigid end product for customization or, in many instances, even for basic service maintenance such as replacement of the resistive element. Such drawbacks are further compounded when unstable resistive materials degrade performance over time and with usage: in the absence of serviceability the only remedy available is to scrap the entire transducer unit and purchase a new one.
While electronic circuit techniques are known for customizing voltage control response to complement a particular transducer configuration, this invention is directed to providing customizing capability in the transducer to avoid or at least minimize necessity of altering pre-existing response setups in the electronic voltage controlled circuitry; accordingly the invention provides, in a novel transducer configuration, the capability of "tailoring" the transducer response characteristic with unprecedented ease and flexibility, under both laboratory and field conditions, to optimize the overall control response characteristic.